I was looking at maintaining activity time by checking the last access time of a file, and when a user was active, it would update the access time of a file.

To try to streamline my code, I wanted to see if 'utime' was faster than 'open/close', so I wrote the following benchmark:

#!/usr/bin/perl -w

use warnings;
use Benchmark;

my $current_time = time();
my $filename = "test.txt";

sub file_open {
       open (FILE, "$filename");
       close FILE;
}

sub stat_change {
       utime($current_time, (stat($filename))[9], $filename);
}

timethese(3000000, {'openfile' => file_open(), 'changestat' => stat_ch
+ange()});
[download]

No matter how many iterations I tried, it always returned really low results:

[11:08:40 jhorner@gateway scripts]$ ./20000619-1.pl 
Benchmark: timing 3000000 iterations of changestat, openfile...
changestat:  0 wallclock secs ( 0.40 usr +  0.00 sys =  0.40 CPU) @ 75
+00000.00/s (n=3000000)
            (warning: too few iterations for a reliable count)
  openfile:  0 wallclock secs (-0.33 usr +  0.00 sys = -0.33 CPU) @ -9
+090909.09/s (n=3000000)
            (warning: too few iterations for a reliable count)
[download]

So, I decided to add a stumbling block to both subroutines:

#!/usr/bin/perl -w

use warnings;
use Benchmark;

my $current_time = time();
my $filename = "test.txt";

sub file_open {
        open (FILE, "$filename");
        close FILE;
        my $i;
        $i++;
}

sub stat_change {
        utime($current_time, (stat($filename))[9], $filename);
        my $i;
        $i++;
}

timethese(3000000, {'openfile' => file_open(), 'changestat' => stat_ch
+ange()});
[download]

The results returned much better, but still not really promising:

[11:10:32 jhorner@gateway scripts]$ ./20000619-1.pl 
Benchmark: timing 3000000 iterations of changestat, openfile...
changestat:  1 wallclock secs ( 0.88 usr +  0.00 sys =  0.88 CPU) @ 34
+09090.91/s (n=3000000)
  openfile:  2 wallclock secs ( 0.91 usr +  0.00 sys =  0.91 CPU) @ 32
+96703.30/s (n=3000000)
[download]

While the benchmark told me that it only took 1 wallclock sec, it really took 10 or 15 seconds.

So, my meditation is this:

Should there be a better method of benchmarking this type
of test, or should I find a better way to benchmark?

The test, while far from infallible, should give reasonable
results.  It doesn't however.  Is 'utime' better than 'open/close'
or vice versa?  Is this all a method of system performance on I/O?

Is this question even worth asking?

jj

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